What size fuse at the positive battery terminal?, I added an inline fuse, but don't know what to use. Options

[PDXMike]

I relocated my battery to my trunk a while back. When I extended all of the wiring from the positive terminal back into the engine compartment I added an inline fuse. It seemed like good insurance in case something shorted out between the battery and the fuse panel. I've been running a 15amp fuse for quite a while without any problems. Tonight, out of nowhere, the fuse blew and left my wife stranded.

Should 15Amps be enough to run all of the accessories? Do I just need to put in a larger fuse, or should I be troubleshooting a short?

The car is a 75 1.8 L-jet. It's pretty stock without any extra lights or stereo amplifiers.

[Mike Bellis]

Where exactly is your fuse installed? 2 of the 4 small red wires go to the fuse panel and ignition switch. You need to figure out which one is which. 1)to the hot all the time fuses. add up those fuse values= the main fuse size. 2) to the ignition switch then to the switched power fuses. add up those fuse values= the other main fuse size. The problem is the factory wires really can only handle 30 amps due to the size. the other two wires on the terminal go to the voltage regulator. If you put a fuse on the main battery cable it should be 200 amps so it does not blow while cranking the engine...

[PDXMike]

The fused link is between the positive battery terminal and all four of the small red wires. The starter lead is not fused.

[messix]

there is no need to "add" a fuse to the battery. the wires to the fuse panel take care of that. the large wire to the starter does not need a fuse. if any thing a 600 amp breaker. unless you added a power circuit to the battery there is no advantage to adding another fuse, it just adds a failure point unnecessarily.

[swl]

There is a lot of unfused wiring in our cars so I can see the desire to put a fuse at the battery. 15 amps though sounds really light depending on which wires are being fused. IIRC there is a 25 Amp fuse on the relay board.

I like the idea of a cct breaker - at least you can reset it at the side of the road. Coming up with a reasonable system rating would be be an interesting exercise. Perhaps just use the rating of the wires carrying the current away from the battery. Really all you are doing is protecting against a dead short that could cause a fire so going high is not a problem.

[Mike Bellis]

there is no need to "add" a fuse to the battery. the wires to the fuse panel take care of that. the large wire to the starter does not need a fuse. if any thing a 600 amp breaker. unless you added a power circuit to the battery there is no advantage to adding another fuse, it just adds a failure point unnecessarily.

Not exatcly true... If our cars were brand new, with new wiring your statement might be true. If the harness is old and modified, fuses are a benefit. The red wires run from the battery to the fuse panel without and circuit protection. If those red wires arc to ground near the fuse panel, the entire harness would melt and may cause a fire. In the case above, I would use four 30 Amp fuses. One on each of four wires. A 30 Amp will hold the load and is the maximum fuse for that size wire. If you do get a short, the fuse will simply blow.

I run a 200 Amp main fuse from my battery disconnect switch. My battery is in the front. The fuse holds just fine. The last thing I want is my 4/0 cable melting in the car.

[r_towle]

I would add one fuse for each line...20 amp should do it.

Rich

[Tom]

Well, the car was designed with a 55 amp alternator, so the designers must have felt that at some point that the car's electrical load would be somewhere near that. I'm surprised that your 15 amp fuse lasted as long as it did. I wouldn't put a fuse larger than 20 amp in the position where you have it now. The better way would be to put in individual fuses on each red wire, fused at 15 amp each. I would also carry some 20 amp fuses just in case.
Tom